Jim Harbaugh, the NFL's reigning Coach of the Year and the face of the 49ers' resurgent franchise, had what the team termed a "minor procedure" performed at Stanford Hospital on Thursday to treat an irregular heartbeat.

Harbaugh, who will turn 49 in December, is expected to return to work Friday in advance of San Francisco's meeting Monday night against the visiting Bears. His players were informed of Harbaugh's medical issue at the end of a walk-through practice late Thursday morning. Assistant head coach and special teams coordinator Brad Seely, who assumed Harbaugh's duties, delivered the news.

"They said it wasn't serious and it shouldn't be a big deal," punter Andy Lee said.

Said linebacker Patrick Willis: "Coach Harbaugh, like he always tells us, he's tougher than a two-dollar steak. We know he's going to be all right."

Based on Harbaugh's brief anticipated recovery time, Dr. Matthew DeVane, a cardiologist based in Walnut Creek, said the second-year head coach "likely" had an electrical cardioversion performed.

The non-invasive, outpatient procedure takes less than a minute and controlled electrical shock is used to reset the heart's rhythm. Patients can resume normal activities the day after the procedure.

According to a team spokesman, Harbaugh began experiencing discomfort Wednesday night and met with doctors at Stanford Hospital. DeVane said Harbaugh probably had atrial fibrillation, the most common abnormal heart rhythm. Typical symptoms can include an elevated heart rate and shortness of breath.

"It can just cause the heart to race and flutter and can make you feel uncomfortable," said DeVane, who is the president of the East Bay Board of Directors for the American Heart Association. "It's a minor procedure and, again, this is guesswork, but it's called a cardioversion where we put the patient to sleep for just a few minutes and give the heart a little zap to try to reset it back into a normal rhythm. It's a very, very common procedure. It's done on an outpatient basis. Usually people are home within two hours and ready to go the next day with no limitations or restrictions."

DeVane said contributing factors include stress, lack of sleep and too much caffeine. Given his occupation, the logical question is how can the wound-tight, workaholic Harbaugh, known for his Sunday sideline screaming, possibly avoid another episode?

Dr. Junaid Khan, a cardiac surgeon based in Oakland, said medication often is prescribed to prevent recurrences in patients with irregular heartbeats. DeVane said such a medical scare can inspire lifestyle changes.

"You can't tell someone to curl up in a ball," DeVane said. "A lot of times, though, this can be an eye-opener for people."

In the 49ers' locker room, players expressed concern, but also smiled as they noted the oddity of being at the facility without Harbaugh on the premises.

"Sometimes I feel like there's five Jim Harbaughs in this building, because he's everywhere," reserve quarterback Scott Tolzien said. "So today it was a little different with everyone wondering, because he's always flying around."

Nose tackle Ricky Jean Francois said players were asking about Harbaugh's whereabouts well before Seely provided the reason for his absence.

"We were wondering that throughout the day because one way or the other you usually hear his voice," Jean Francois said. "The breakfast room. The training room. You're going to see him somewhere around here."

The assumption is Harbaugh will return to the facility Friday, five days after the 49ers' 24-24 tie with the Rams. His absence Thursday was shocking, but his believed ailment was minor enough for DeVane to joke about its cause.